Terminal for resistance conductors



Oct. 15, 1929. w R. KING TERMINAL FOR RESISTANCEl CONDUCTORS Filed July 7, 1928 A'TTORNEY Patented Oct. 15, 1929 UNITED STATES PATENT osmosi.

"WILLIAM KIN?, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T WESTINGHOUBE ELECTRIC MANUFACTURING COMPANY, A. CORPORATION 0F ENNSYLVANIA.

lTERMINAL FOR RESISTANCE CONDUCTORS Application led July 7,

This invention relates to electric heaters and particularly to terminals for resistance conductors.

An object of the invention is to provide a terminal for resistance conductors that shall be simple in construction, eiiicient in its o eration and easily manufactured and insta led.

Another object of the invention is to provide a terminal for electric conductors that may be expanded -into electrical contact with 'the conductor.

A further ob'ect of the invention is to provide a terminal for sheathed electrically-in sulated conductors that may be expanded into electrical contact with the conductor after the conductor has been located in the sheath.

A still further ob'ect of the invention is to provide a terminal for electric conductors in which contact is established both by the expanding. of the terminal into contact with the conductor and by pressing the conductor f against the terminal; and A still further object of the invention is to provide terminals for resistance conductors in which contact between the terminaland the conductors may be established by pressure.

For a fuller understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, in which Figure 1 is a plan view, partially in section, of a terminal for an electrical-resistance conductor;

Fig. 2 is an end view thereof l;

Fig. 3 is a plan view pf a detail embodied in the terminal of Fig. 1f

Fig. 4 is an end'view of the detail shown in Fig. 35

Fig. 5 1s -a plan view of a moditied form of the detail shown in Fig. 3;

Fig. 6 is an end view of the in Fig. 5;

Fig. 7 is a view, in longitudinal section, of an autoclave in which a tubular heater is positioned to be subjected to an atmosphere of steam to convert magnesium metal into magnesium hydroxide;

detail shown 1928. vSerial No. 291,048.

Fig. 8 is a view, in section, of a portion of sa heating unit completely assembled and ready for use after it has been treated in the autoclave shown in Fig. 7

Fig. 9 is a plan lview showing a modification of the terminal structure illustrated in Fig. l; and

Fig. 10 is an end View thereof.

In the drawing, a terminal 1 for an electrical-resistance conductor 2 is illustrated, which is particularly adapted to'sheathed, encased or tubular heating units (see Fig. 8). The terminal 1 comprises a hollow cylinder having a threaded end portion 3, a split end portion 4 and an intervening enlarged portion 5 which may be provided with a knurled surface for a purpose to be hereinafter set forth.

The terminal 1 may be secured to the helix 2 by insertin a metallic pin 6 of oxidizable material, suc as magnesium, into the split end portion 4 and then inserting this end l ortion into the helix. The terminal, having een located as shown in Fig. 1, the pin 6 of magnesium metal may be converted to magnesium hydroxide by subjecting it to the oxidizing effect of steam underI pressure. Magnesium metal, when .oxidized in this manner, expands and increases its dimensions approximately 100 percent over its dimensions in the metallic state. As a result of the expansion of the magnesium hydroxide, the split portion 4 of the terminal is expanded or pressed firmly into engagement with the turns of the helical resistor 2.

As shown in Fi 3 and 4 of the drawings, the body portion sand the head of the in 6 are substantially circular in section. owever, the body portion may be oval or elleptical in section, as shown in Figs. 5 and 6.. If the body portion of the pin 6 is made elllptical or oval in section, as shown in Figs. 5 and 6, the pin may be wedged between the spllt portion 4 of the terminal and still leave clearance between the Walls of the split portion 4 and the body portion of the pin so that steam may pass therethrough to convert the pin to magnesium hydroxide.

The terminal construction, shown in Fig. 1, is particularly adapted to tubular heating elements of the type shown in Figs. 7 and 8. In Fig. 7 of the drawing, a heatingelement 9 is illustrated in the process of manufacture, and, in Fig. 8, the heating element 9l '10 serted into the ends of the helical resistor 2,

a` tube or sheath 11 enclosing the resistor 2 and the portions 4 and 5 of the terminals, and a helix 12 offmagnesium'fmetal,'centrally located about the terminals and resistor an 15 placed within the sheath or tube 11.

In order to convert the pins 6, the core 10, and the helix 12 to magnesium hydroxide, the` heating element assembly may be placed in an autoclave 13, one end thereof being wedgedly secured in an aperture 14 provided in a partition wall 15. Steam may be admitted' into a compartment 16 to the left of the partition 15 through a valve 17 and discharged into a chamber 18 to the right of the partition 15 and exhausted therefrom through a valve 19. Steam, entering the chamber 16,

through the valve 17 will flow through the tube or sheath 11 and through an opening 21 in the terminals 1, as indicated by the arrows lin Fig. 7. When the magnesium pins 6, the magnesium core 10 and the helix 12 have been subjected to an atmosphere of steam, maintained at a pressure .of a predetermined value for a predetermined length of time, the magnesium metal is converted into magnesium hydroxide. The hydroxide of magnesium may then be changed to magnesium oxide by subsequently heating the heating element in a furnace to evaporate the 40 water contained in the hydroxide.

' The magnesium metal, when so oxidized,

expands and fills the space between the resistor and the walls of the tube 11 compactly, as shown in Fig. 8. As there shown, the pins 6 expand, when converted to oxide, causing the portions of the split end 4 to be expanded or spread apart and press tightly against the end turns `of the helical resistor 2. It 1s to be noted also th`at, since the magnesium helix 12, when oxidized to magnesium oxlde, completely fills the spacel between the walls of the tube 11 and the ends of the helical resistor 2 in contact with the terminal portions 4, the end Vturns ofthe helicalresistor will `be pressed against the s lit end portions 4 of the terminals, thereby increasing the pressure exerted between the helical resistor and the terminals by means of the oxide produced by the pins 6. l'

i Since the portion of the magnesium helix `i12 surrounding the enlarged portion 5 of the terminal 1, tends to oxidize more quickly than the magnesium located to the right thereof,

e the space between the tube andthe portion 5 will be filled by the converted magnesium.

thereby restricting the flow of steam through the tube. But, as the terminal 1 is provided with the opening 21, steam will flow through the opening 21 and escape through the tube or sheath 11 by way of the split portion"4 of the terminal, whereby complete oxidation of the magnesium is insured.

lhile I have indicated that the split end portion 4 of the terminal 1 may be expanded by chemical means', that is, by means of a pin of metallic magnesium placed in the end thereof and oxidized, whichupon oxidizing expands the split portion 4 into engagement with the resistor helix 2, it is to be understood `that the split portion 4 of the terminal may be expanded by mechanical means.

` Since the portion 5 of the terminal 1 is knurled, the oxide12awill embed itself in the surface of this portion and hold the terminal firmly in position in the tube, as shown in Fig. 8. lVhen the tubular heating unit 9 has been completely treated in the manner hereinbefore set forth, the ends of the tube may be filled with a cement 23, such as water glass. The oxide 12a is then protected from 4the moisture of the atmosphere and is also prevented from being broken and escaping fromv the tube 1l.

In some instances, it may be desirable to provide the split portion 4 of the. terminal 1 With screw threads 24, as shown in Fig. 9. If

verted to magnesium hydroxide, and t t the Y,

terminals are secured firmly. to the tube or sheath 11 by the expansively oxidized magnesium provided by the helix 12.

The oxidel produced by the helixl 12 expands within the tube 11 and, in addition to holding the terminals 1 firmly in place, presses the resistor against the split portions 4 of the terminals.

The oxide of magnesium provides the proper insulation between the resistor element, the terminals. and the tube 11, and, also, an efficient path for the flow of heat from the resistor to the tube. u i

As various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof, yit is desired that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims;

I claim as my invention:

1. The method of securing a terminal having a split end portion to a helioallywound resistor, which comprises inserting a pin of metallic magnesium in the split portion, lo-

cating the split portion inside of a helicallyg Wound resistor and subjecting the assembly to the action of steam under pressure to change the metallic magnesium into magnesium hydroxide and cause it to expand and Wedge the split portion in the resistor helix.

2. The method of securing a tubular terminal having a longitudinally split end portion to a helically-wound resistor adapted to be located in a tubular casing, which comprises the steps of locating a pin of magnesium in the split end portion of the terminal, locating the terminal in an end portion of a helically-Wound resistor, locating an open helix of metallic magnesium around the resistor and terminal, ,locating the assemblv Within a tubular casing and subjecting it to the action of steam under pressure.

3. A terminal structure for a tubular heating unit having a tubular casing and a helioally-Wound resistor therein, said terminal including a tubular metal member having a longitudinally-split end portion adapted to be located Within a helically-Wound resistor, and electric-insulating material expansively oxidized in situ, Within and around the split end portion to hold the terminal in proper operative position in a casing and to clamp it in engaging relation With a resistor.

In testimony whereof, I have hereunto subscribed my name this 26th day of June, 1928.

. WILLIAM R. KING. 

